There are several factors to consider with natural lighting. If it comes via a clear window (rather than a light tube) then there will be:

the possibility of solar heating / overheating

the insulation values of windows are usually much poorer than of plain walls (in a well insulated house) so more natural light will mean more heat escaping

there may be shading and reflection from outside surfaces

the shape of rooms, particularly the depth will affect how well light penetrates into the house

If it comes via a light tube or optic fibres then there are several issues to look at

the question of the amount of light that is actually achievable (which is easy to overestimate)

the routing of tubes or fibres through the building structure (relatively easy with fibre but can be very difficult with light tubes). Optic fibre lighting is a relatively new technology and any comments from people who have used it as to how well it actually works would be most welcome here. One of the suppliers is the Swedish company Parans

there is a large cost consideration (compared with electric lighting)

there is a rather uncertain value to be placed on ‘natural’ lighting.

Artificial lighting

Artificial lighting is a major user of domestic energy and deserves careful consideration because it is a complicated subject when it comes to design. The main factors are:

the purpose of the lighting

the energy consumed by different types of electric light sources

the intensity of light required

the aesthetic and qualitative aspects

ways of controlling and switching those lights

levels of maintenance

LCALife Cycle Analysis (also sometimes called 'Cradle to Grave' or 'Cradle to Cradle' assessment) see Building materials of materials used

Purpose and function

Lighting is usually employed for one or more of the following reasons.

This depends on the type of ‘bulb’ or tube in the light fitting and ranges on a scale shown below with fluorescent tube (typically the 1500mm and 2400mm long) being the most efficient and the normal (incandescent) light bulbs the worst. These bulbs are being phased out over much of the world and will soon be unobtainable in the EU.

US Energy Information Administration ratings

Efficacy is the measurement of how many lumens of light you get per watt of energy used and the list looks like this:

big fluorescent tubes, especially T8 tubes with an electronic ballast have an efficacy of 80-100 lm/W

compact fluorescent lights (low energy bulbs) 45-60 lm/W

quartz halogen lights 24 lm/W

incandescent bulbs 14 lm/W

white ledslight emitting diodes 10-170 lm/W (LEDs vary greatly.) They are improving rapidly and the US Energy Information Administration claims that the average efficiency of white LEDs reached nearly 100 lm/W in 2014 and since then they have improved significantly. However most of the LED bulbs (typically the 3 watt ones) you see in the shops in 2018 are actually about 80 lm/W. (See Wikipedia on the subject). LED strips are proving to be very economical in situations where they can be hidden such as behind shelf nosings in kitchens.

Compact fluorescent lights are 3 to 4 times more efficient than incandescent bulbs but not as good as long fluorescent tubes.

Light intensity

Lighting levels will often be a matter of a combination of past experience and playing around with different sizes of bulbs in lamps. However, one way to approach the actual choice of lighting is to first work out the brightness of light needed in a particular area and then decide on how important the aesthetic considerations are.

The human eye has an incredible ability to adjust to varying levels of light so that it is very difficult to gauge the amount of energy falling on a surface. For instance when you are reading a book in bright sunlight there may be 100,000 lux falling on the page. Read the same book under a bright electric light and there might be about 500 lux falling there, i.e. only 1/200 of the energy intensity but it will still look bright.

You can do a bit of research to find out which light fittings emit what kind of levels of light by buying a light meter and doing a few tests on light fittings, luminaires, shades etc. Light meters range enormously in price but you can get hold of a basic model for less than £25 which will give readings in lux.

Remember that when light travels out from a lamp (a lamp without a reflector, that is), its intensity drops off as the cube of the distance from the bulb, and as the square from a long tube (roughly). So if you hold a light meter half a metre away from a bulb and it gives a reading of 400 lux and then you take a reading 1 metre away it will give a reading of 50 lux (twice the distance so divide by 2x2x2). This means you have to be careful about measuring exactly how far away you hold the meter because the brightness drops off disproportionately quickly.

It also means that the height at which lights are placed in a room is crucial for the brightness. (and for glare – see below)

The aesthetics and quality

This depends on several factors:

the colour temperature of the light

position, directionality, contrast and glare of the light

flicker

appearance of the luminaire

Colour temperature

This is the name given to the quality of colour due to the wavelengths of light put out by the lamp and results in ‘cold’ and ‘warm’ effects and a tendency towards an emphasis of colours such as yellow, green and pink. Sometimes tinges of these colours can be seen in the light from compact fluorescent lamps, particularly the older models. While natural daylight has a very broad spread of wavelengths, fluorescent tubes and LEDs tend to have very specific frequencies that they emit and the manufacturers try to blend several of these frequencies in one lamp to achieve a reasonable balance.

Incandescent and quartz lamps give the better colour renderings because they emit a wide, balanced range of wavelengths but they also happen to be the most wasteful of electricity.

You can choose fluorescent tubes with various colour temperatures to achieve different effects. For instance ‘warm white’ tubes with a colour temperature of 3000K will give a warm effect while ‘extra warm white’ with a colour temperature of 2700K give an even more cosy effect. ‘Cool white’ is what is usually used in offices and workshops and ‘Daylight’ (so-called, at 6500K) is used where it is important to get accurate colour matchings such as artists’ studios. Recently a new tube has come on the market with a colour temperature of 17,000K. This tube emits a high proportion of cool light and approximates well to natural daylight (18,000K). Tests so far, mainly in office environments, have indicated that people feel energised and refreshed by this type of tube. It is claimed that it helps balance a person’s circadian rhythms.

Position, directionality, contrast and glare

Obviously, what people consider to be an area well lit varies from person to person. However there are some useful guidelines.

The relationship between the observer, the light source and the area being viewed is paramount. At worst, the lighting causes glare, and the parts of a room or house you want to see are poorly lit. At best, the area you want to look at is clearly and attractively lit and the source of light is unobtrusive unless it is itself a thing of beauty.

Modelling is the name of the quality that lighting can give when it provides a very clear shape of objects. This is usually caused by the light being mono directional (maybe spot lights), often at roughly 45° to the vertical. It is like bright sunlight which creates strong shadows and powerful contrast: the opposite to bland overall ceiling lighting. This is comparable to theatre stage lighting as viewed by the audience. The problem of course is that as you walk round the area you become like the actors who are blinded by the spot lights. It is very difficult to make it work from all angles and all positions.

Flicker

The problems with flicker can be easily rectified by using high frequency ballasts. This type of fluorescent light is flicker free to the human eye and starts almost instantly. (It also avoids flicker when it is failing). Not only that, they are over 20% more efficient than normal fluorescent lights and the tubes last longer. Also they do not hum or buzz like normal ones sometimes do. The tubes also last considerably longer and they are dimable. In every way better except for the cost which is a bit higher (probably about 10 extra for this type of ballast). It is possible to convert existing fluorescent fittings by changing the starter and choke for high frequency control gear.

Lighting design

Making internal lighting attractive, functional and low energy is probably one of the greatest challenges. Even with old fashioned bulb lighting most people have little idea how to get the best effects. With low energy lights there is still a dearth of good lamps that they work with. Try out a trip round IKEA, (or Habitat) or a good local lighting store and try to buy a lamp which will accomodate a 20W low energy bulb. They are often too long to fit into the shade or fitting.

The problem with designing lighting, and in particular low energy lighting, is that the most obvious straightforward way of lighting a room, one big lamp hanging from the centre of the ceiling, is also (with one or two exceptions) likely to be the least useful and probably the most ugly approach. This is because most activities take part round the edge of a room so with a centre light, people are working in their own shadow or suffer glare. It is also almost impossible to create differing effects (except dimming) with a centre light. However, the alternative of having several smaller and varying types of lighting around the edge of a room risks two drawbacks: that sockets for the lights will be in the wrong place and that you need to walk round the room turning individual lights on and off all the time.

Lighting where you want it

There is a way round this problem, borrowed from the US idea of ‘mood lighting’ and the self builder is in an ideal position to take full advantage of this because of being able to easily install extra lighting circuits. This is something that commercial house builders very rarely do and can lead to excellent results at little extra cost.

The idea is that you have an extra circuit (shown in green) which you run around the room at low level or waist height a bit like the normal power sockets. You provide plenty of socket outlets for lamps to plug into.

In this way it is possible to control several lights at once from one normal light switch. Because it is a lighting circuit it will normally be in 1 mm. cable with a 5amp circuit breaker (rather than 2.5 mm. cable) so some way is needed to prevent people accidentally using it as a power circuit and plugging in larger equipment. This can be done by fitting small round 5amp sockets and then wiring the lamps with small round 5amp plugs so that only these lamps can be used with the sockets.

These sockets and plugs are smaller and less obtrusive than 13amp ones and you can afford to place them anywhere that a lamp might be required. With this arrangement there is a variety of types of lighting available, – table lamps, adjustable desktop lights, standard lamps, uplighters etc. In this way it is possible to achieve exactly the effect you want while using low energy bulbs. Of course individual lamps can be switched off when not needed, while the rest are left on. Lamps can be swapped around.

When buying light fitting try to avoid shades which kill off much of the light. For instance most paper lamp shades actually absorb more than 50% of the light before it gets out, especially by the time they have attracted the inevitable layer of dust. That makes no sense if you are trying to be efficient with energy. (However if the inside of the shade is bright white or polished then most of the light will get reflected out and into the room).

Dark areas

Sometimes a house will have areas which seem to be permanently dark and gloomy and require serious brightening up. The most energy efficient lighting is the large diameter fluorescent tube, (T8 range), usually 600mm, 1200mm, 1500mm or 1800mm.

The objections people have to these types of light are fourfold; they flicker in use, they flicker when they are switched on, they give a peculiar colour of light and they have bad connotations of workplaces, supermarkets etc. The problems with flicker can be easily rectified by using high frequency ballasts. This type of fluorescent light is flicker free to the human eye and starts almost instantly. (It also avoids flicker when it is failing). Not only that, they are over 20% more efficient than normal fluorescent lights and the tubes last longer. Also they do not hum or buzz like normal ones sometimes do.

The tubes also last considerably longer and they are dimable. In every way better except for the cost which is a bit higher (probably about £10 extra for this type of ballast). It is possible to convert existing fluorescent fittings by changing the starter and choke for high frequency control gear. The colour of the lighting is corrected by using a tube with the appropriate colour temperature The utilitarian appearance of fluorescent lights is usually the main problem in a domestic setting. There are three approaches to this

Use stylish luminaires; either the higher end of commercial products or do a search for the sort of thing individual designers are producing. However this is a very limited market. Use indirect recessed luminaires preferably with louvres so that the fitting is not obvious; only the light

hide the fitting with a pelmet or in a recessed area which has a reflective internal surface. This latter can give a very pleasant effect of a shadow line with the ceiling appearing to ‘float’ separately from the wall. If the wall is painted a light colour it is an excellent way of creating brightness without glare. In such situations it may be necessary to use the sort of reflectors that are generally used over aquariums.

A further way of making these high frequency lamps even more efficient is to fit an automatic dimmer which responds to daylight levels so that as it gets dark on an evening the light automatically turns itself up. If you add a PIR detector to this then it will only go on when there is someone in the room. With this setup the light comes on gradually over a couple of seconds. This makes for an incredibly efficient combination.

Optic fibre lighting

Comments are invited on how well ducted optic fibre lighting actually works. It is quite a recent technology and there seems to be little track record but holds a possibility for considerable energy saving. Please use the comment form below. One of the companies producing this is Parans of Sweden.

Fire safety

Where light fittings are recessed into ceilings which have a floor above, there is the danger that the structural integrity of the floor has been compromised in case of fire. There are special covers available, usually intumescent material, which are installed above the light fittings and they seal off the route that fire and smoke might take.

Building Regulations

The Regulations state that with new dwellings there must be a certain amount of low energy lighting and this is used in the DERDER is the Dwelling CO2 Emission Rate expressed as kgCO2/(m2.year).
calculation.